Numerical results demonstrated that the proposed integrated IRS-BS architecture can achieve significant performance gain over the conventional multi-antenna BS without integrated IRS. It was also shown that the developed IRPA can outperform other benchmark algorithms in terms of sum-rate under the case without perfect CSI, and approach the performance upper bound with perfect CSI as the training overhead increases. Moreover, the double-reflection channel components were shown to have a more dominant impact on the achievable sum-rate than the single-reflection channel components due to the short inter-IRS distance and the significantly larger number of double-reflection channel components. Finally, the number of antenna modules in the generalized IRS-BS architecture was shown to have a significant influence on the system rate performance, which should be properly selected in practice to balance the communication performance and implementation cost. It is noteworthy that this paper is an initial study of integrating IRSs into BS/AP, while the results can be extended to other promising directions in future work, such as considering practical IRS phase-shift model [1]}, IRS passive reflection optimization in frequency-selective wideband channels, joint optimization of IRS passive reflection and user transmission scheduling, IRS passive reflection optimization based on statistical CSI to reduce the training overhead, and so on.
